Media can get stranded at the offsite vault for the following reasons:
A backup tape appears on the Picking List for Vault and Distribution List for Robot only once. If a tape from that report is missed and is not returned to the robot, it never again is listed for recall.
You change offsite volume group or pool names. For example, if you begin to use a new media type, you have to use a new volume pool name. If you change names, media may be stranded offsite because the Picking List for Vault is based on offsite volume pools and offsite volume groups. Media associated with the old names is not be listed.